1. Field of the Invention
The present invention relates to petroleum reservoir characterization through geological modelling. More particularly, the invention relates to a history matching method through gradual modification of an image representative of the petroleum reservoir, for considering seismic data and dynamic data such as oil production, water production, gas/oil ratio (GOR), water cut, seismic impedances, etc.
2. Description of the Prior Art
Optimization and development of petroleum reservoirs are based on the most accurate possible description of the structure and of the petrophysical properties of the reservoir being studied. a tool implemented on a computer is used for accounting for these two aspects in an approximate way known as a geological model. A geological model is intended to best account for the structure and the petrophysical properties of a reservoir. The geological model has a grid pattern that forms the frame of the reservoir and that has to be representative of the structure and three- or two-dimensional petrophysical property maps (or images) associated with this grid, that have to be representative of the static or dynamic behavior of the reservoir.
In the petroleum industry, it is very important to characterize reservoirs using dynamic data such as the production data or 4D seismic data. Geostatistical methods are often used to construct a reservoir heterogeneity map. In this context, the maps are referred to as “geostatistical realizations”. They are generated on a random basis by a computer and do not generally allow the production and/or seismic data to be calibrated. To constrain these maps (realizations) by the measured data, it is necessary to parametrize the maps in order to subsequently apply an optimization method to minimize a calibration criterion representing the differences between simulation results and measurements. Parametrizing an image or a realization within the context of geostatistical methods defines a parameter whose modification allows a new image to be obtained. A parameter is thus generally associated with an image construction or deformation method based on this parameter.
Several methods have been proposed to parametrize geostatistical realizations. The gradual deformation method presented by Roggero, F. and Hu, L. Y.: “Gradual Deformation of Continuous Geostatistical Models for History Matching”, paper SPE-49004, Proc. SPE Annual Technical Conference and Exhibition, New Orleans, 1998, introduces a parameter that allows combining two geostatistical realizations to generate a new realization that varies from one existing realization to the next, while keeping geostatistical coherence. This method is a global approach that does not account for the objective function variations in local regions.
To improve this approach, the local gradual deformation method presented by Hu, L. Y.: “Gradual Deformation and Iterative Calibration of Gaussian-Related Stochastic Models”, Mathematical Geology, Vol. 32, No. 1, 2000, allows combining two geostatistical realizations in predetermined local regions. The regions are defined by stratigraphic grid cells. The geometrical domains of these local regions do not change during an optimization process.
Another method for accounting for local impacts, referred to as the “patchwork method”, is proposed by COSTA REIS, L.: “Intégration des Données Dynamiques Dans un Modéle Géostatistique de Reservoir”, Ph.D., Université Paris 6, 2001. According to this approach, several realizations are generated. Dynamic data are simulated thereafter by means of a computer based reservoir simulator. A new realization is then generated by combining existing realizations on the stratigraphic grid cells, according to the objective function values in local regions. The absence of parametrization of this approach does however not allow applying an optimization method to facilitate history matching.